This invention relates to information processing apparatus comprising a memory means for writing information into the memory at times depending on first timing signals, and means for reading information out of the memory at times depending on second timing signals which drift in and out of phase with the first timing signals. The invention was conceived when designing a picture synchronization system for television signals.
Many forms of television picture processing depend for their operation upon the storage of one or more fields of the signal. Examples of types of picture processing which employ storage are: standards conversion; picture synchronization; noise reduction; and picture size reduction and expansion.
Picture storage can be carried out using analog methods, the use of quartz delay lines being an example of this type of storage. However, digital memories are cheaper, more reliable and more compact and most equipment employing picture storage now uses digital semiconductor memory chips with the television signal being converted from analog-to-digital form at the input of the equipment and back to analog at the output.
This invention is particularly, although not exclusively, applicable for use in a picture synchronizer. The purpose of a synchronizer is to re-time a television signal, e.g. one arriving from an outside broadcast, so that its subcarrier, line and field frequencies are identical to some local reference, e.g. the studio camera pictures. At the output of the synchronizer the remote signal can be treated as if it were generated locally and can be mixed, faded, and inserted into local pictures without causing timing disturbance to the transmitted signal.